Unfortunately, there is no way to claim those Medical Expenses which were incurred in 2019 on your 2018 tax return.
Keep in mind that claiming those medical expenses is not going to reduce your income, which is what your benefits are based on. Claiming Medical Expenses on your tax return only reduces your tax payable and will have no effect on the benefit calculation. Sadly it looks like you are stuck with reporting that income on the 2018 tax return, and the medical expenses claim in 2019.
